DESCRIPTION: (Adapted from abstract) The goal of this proposal is to understand how mRNA stability is controlled. It is now clear that mRNA stability has a significant impact on the control of eukaryotic gene expression. In fact, alterations in the normal decay rate of specific mRNAs has been found to lead to particular human diseases and cellular transformation. The goal of the proposed research is to understand how specific sequence element within mRNAs control mRNA decay rates using budding yeast as a model eukaryotic system. Both stable and unstable mRNAs are degraded by a common decay pathway suggesting that the same general decay machinery acts on all mRNAs but is controlled by specific elements within transcripts to give rise to different mRNA decay rates. The proposed research will determine the molecular mechanism by which one of these instability elements located with the 3'UTR of the unstable MFA2 mRNA promotes decay. The gene products that specifically recognize this instability element and modulate decay will be identified through two genetic strategies. In one approach genes required by this element to promote instability will be identified by screening for mutations that stabilize a reporter gene carrying the MFA2 3'UTR. A complementary strategy will be used to identify wild-type gene products that when over expressed suppress the stabilizing effect of mutations in the MFA2 instability element. Genetic analysis will be used to determine whether the identified genes correspond to enzymes known to be involved in this decay pathway or are new factors which specifically function to control mRNA decay. The genes for the identified control factors will be cloned and their sequence analyzed to determine if they share sequence similarity with known protein functional domains. The function of these gene products will be determined in vivo by defining the step in the decay pathway at which these products act, examining whether they are specific or general control factors, and determining whether they specifically bind to the MFA2 instability element. These studies will provide insight into how specific sequence elements modulate the decay machinery to control mRNA decay rates, a general principle of eukaryotic mRNA decay.